1. Technical Field:
This invention relates generally to luminescence techniques for radiation dosimetry, and, more specifically, to rapidly determining an unknown absorbed dose of radiation using optically stimulated luminescence.
2. Background:
Following its first demonstration as a dating tool by Huntley et al.,.sup.1 optically stimulated luminescence (OSL) has developed into a popular technique among the geological dating community for the determination of equivalent doses in natural materials. The utility of the technique relies on the fact that the thermoluminescence (TL) signal from many natural materials is sensitive to light, and exhibits such light sensitive effects as light-induced fading, and phototransferred TL (PTTL). By exploiting this light sensitivity one can examine not only the loss of TL as a function of light exposure, but also one can monitor the luminescence emitted during light exposure, and use this luminescence signal as a dosimetric probe.
The application of OSL in personal and environmental dosimetry has been much less frequent. Although most of the popular TL materials exhibit light-induced effects there has been little exploitation of this as a dosimetric tool..sup.2 The main problem in OSL dosimetry arises from using a high intensity laser to stimulate an irradiated sample of a luminescent material compared to the very low intensity of luminescence that is to be detected from the material. Even the best interference filters and mirrors, like notch filters in combination with glass filters, partially transmit the intense laser light, and this leakage of stimulation light can be stronger than the OSL intensity by several orders of magnitude.
OSL measurements may be performed in two basic configurations--continuous wave (cw) or pulsed. In cw measurements, the luminescence is continually monitored during optical stimulation until all of the trapped charge is depleted. In existing pulsed OSL measurements, the luminescence is detected during the stimulating light pulse. However, existing methods for measuring OSL during continuous wave or pulsed light stimulation suffer from significant background signal interference caused by stimulation light leakage. Decreasing the stimulation light intensity results in longer data acquisition time requirements because the total luminescence output in general depends on the total amount of light delivered to the luminescent material.
It is thus an object of this invention to provide a method for achieving fast measurements with high sensitivity over a wide dynamic range of radiation doses without encountering significant background signal interference or stimulation light leakage.